1. Field of the Invention
The present invention relates to a reservoir tank for storing a liquid, and in particular to a reservoir tank whose bottom structure is improved.
2. Description of the Related Art
There is a reservoir tank for storing a liquid. It is necessary to seal the inside of the reservoir tank in order to prevent the stored liquid from leaking. If the bottom of the reservoir tank corrodes due to deterioration and so forth, the liquid is likely to leak therefrom. For the purpose of preventing the stored liquid from leaking out of the reservoir tank, various ideas are conceived regarding a bottom structure of the reservoir tank, such as described in Japanese Patent Laid-Open Publication No. 9-272991, for example. The Publication No. 9-272991 relates to an electric anticorrosion method for an outer surface of a tank bottom plate to be placed on an asphalt sand. With respect to this method, linear insoluble electrodes are arranged on the asphalt sand in a lattice state. A conductive material is laid over the whole surface of the asphalt sand so as to cover the insoluble electrodes. Further, a sand layer is formed on the conductive material. The insoluble electrode is connected to a plus side of a DC power supply and the tank is connected to a minas side thereof to supply a predetermined anticorrosive current to the outer surface of the tank bottom plate.
However, as for the electric anticorrosion method of the above-noted publication wherein an external power-supply system is adopted for the outer surface of the bottom plate of the outdoor tank, it is necessary to lay the linear insoluble electrodes on the asphalt sand, on which the reservoir tank is placed, in the lattice state. Thus, there arise problems in that an installation operation takes a lot of labor and the cost increases. In a case of the outdoor-type reservoir tank having a large size, it is impossible to transfer it through a general rode. Therefore, welding for assembly is performed at a place for setting the reservoir tank. Sometimes it is impossible to deal with the reservoir tank such as described in the above-noted Publication No. 9-272991. Further, it is difficult to externally check the liquid leaking out of the bottom. In case the liquid leaks out of the bottom, there arises a problem in that the leakage liquid pollutes the underground.